Kent police is to apply to the courts for more time to investigate claims that Conservative party activists breached election laws while fighting off a challenge from the Ukip leader, Nigel Farage.
It is believed to be the 11th force investigating claims that the party has misallocated spending during the 2015 general election campaign.
The Conservatives have previously denied any wrongdoing and say all its election expenses complied with the law.
But senior Tories admit that the inquiries, sparked by a Channel 4 News investigation, have become a “significant inconvenience” for the party in the middle of a divisive and fraught campaign to remain in the EU.
Kent police was among several forces who attended a meeting last week with the Electoral Commission and the Crown Prosecution Service to discuss the issue.
Detectives from Kent are focusing on the battle for South Thanet, when dozens of Conservative activists were bussed in to the area to combat Ukip activists.
The claims centre on whether the expenses run up by the Conservatives in the South Thanet campaign were properly reported to the Electoral Commission.
General election campaigns allow candidates to spend between £10,000 and £16,000 depending on the size of the electorate. In South Thanet, the Conservative candidate Craig Mackinlay said his campaign spent just below the limit of £15,016.
Under election laws, any costs incurred to promote a candidate must be declared on local candidate spending returns.
Receipts showed that £18,000 was spent accommodating Conservative party workers in the Royal Harbour hotel in Ramsgate, and a Premier Inn in Margate, which were not declared on the spending return. Instead, they appear on the Conservative party’s national expenses – normally reserved for party-wide costs.
A further £715 was spent on the Alpha hostel, used to accommodate a busload of activists who took part in a “Stop Farage” campaign. The costs for the hostel do not appear to have been declared.
Ten other police forces have announced they are examining candidate spending. These are Cheshire, Gloucestershire, Greater Manchester police, Lincolnshire, Northamptonshire, Nottinghamshire, Staffordshire, Warwickshire, West Mercia on behalf of Devon and Cornwall, and West Yorkshire.
Under electoral law, any claims made about the conduct of an election would have to be made within 12 months of the ballot unless there are exceptional circumstances.
A spokesman for Kent police confirmed they were seeking an extension, adding that no date had yet been set for its application to the court.
This article was written by Rajeev Syal, for theguardian.com on Monday 16th May 2016 15.08 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010